This invention relates generally to systems for recording signals on motion picture film, and, more particularly, to systems for recording a continuous time code signal on such film while it is being intermittently advanced by a motion picture camera.
Motion picture film editing normally requires the accurate synchronization of motion picture film with an accompanying sound recording. The film can come from several different cameras operating simultaneously, and the sound recording can include a number of tracks for dialogue, music and appropriate sound effects. It is ordinarily essential that all of the film and sound tracks be arranged in precise synchronization with each other.
Synchronization is relatively easy when editing video tape, as contrasted with motion picture film, because a time code signal can be recorded in a separate time code channel adjacent an edge of the tape. Knowing the exact time at which a particular video frame was recorded makes it relatively easy to synchronize it with other video and audio tapes that record similar time code signals.
Editing motion picture film, on the other hand, has generally been more difficult, because devices have not been available for recording such continuous time code signals on the film. Generally, the film has been synchronized with the various sound tracks by means of a clap stick and its resulting sharp noise. It is believed that one reason such time code signals have not been recorded on motion picture film is because of the anticipated difficulties in recording a continuous signal having a substantially constant bit rate on a medium that moves in an intermittent fashion.
Some prior systems utilized film having a latent digital code signal recorded in a margin of the film prior to its use in a camera. However, since the code was pre-exposed in the film, it could not indicate the actual time at which the corresponding picture frame is exposed.
Another prior system includes a special recording apparatus that records a 12-bit code on the film at the same time it is being intermittently advanced by a camera. The bits are recorded only in the mid-portion of each frame, at a time when the film is being advanced at a substantially constant rate. The system is specifically designed so as not to record near the edges of the frame, when the film is rapidly accelerating or decelerating. The system therefore does not appear to be useful for recording a time code signal that is continuous, without any gaps between its successive bits.
It should therefore be appreciated that there is a need for a system that can record a continuous time code signal on motion picture film, to facilitate a subsequent synchronizing of the exposed film with an associated sound track having the same time code signal recorded on it. The present invention fulfills this need.